WO2013/136220 incorporated herein by reference, discloses a printing process which comprises directing droplets of an ink onto an intermediate transfer member (ITM) to form an ink image at an image forming station, the ink including an organic polymeric resin and a coloring agent (e.g. a pigment or a dye) in an aqueous carrier. The intermediate transfer member, which can be a belt or a drum, has a hydrophobic outer surface whereby each ink droplet spreads on impinging upon the intermediate transfer member to form an ink film. Steps are taken to counteract the tendency of the ink film formed by each droplet to contract and to form a globule on the intermediate transfer member, without causing each ink droplet to spread by wetting the surface of the intermediate transfer member. The ink image is next heated while being transported by the intermediate transfer member, to evaporate the aqueous carrier from the ink image and leave behind a residue film of resin and coloring agent which is then transferred onto a substrate.
The present invention is concerned with the construction of an intermediate transfer member that may be employed in such a printing process but may also find application in other offset printing systems. The intermediate transfer member described in the afore-mentioned applications may be a continuous loop belt which comprises a flexible blanket having a release layer, with a hydrophobic outer surface, and a reinforcement layer. The intermediate transfer member may also comprise additional layers to provide conformability of the release layer to the surface of the substrate, e.g. a compressible layer and a conformational layer, to act as a thermal reservoir or a thermal partial barrier, to allow an electrostatic charge to the applied to the release layer, to connect between the different layers forming the overall cohesive/integral blanket structure, and/or to prevent migration of molecules there-between. An inner layer can further be provided to control the frictional drag on the blanket as it is rotated over its support structure.
At the image forming station, it is important to maintain a fixed distance between the surface of the ITM and the nozzle of the print heads that jet ink onto the surface of the ITM. Furthermore, as printing is performed by multiple print bars staggered in the direction of movement of the ITM, it is important to ensure that the ITM does not meander from side to side if correct alignment is to be maintained between ink droplets deposited by different print bars. The problem of accurate registration may prove more severe as the dimensions of the belt increase and/or when the belt is not mounted on solid supports over a significant portion of the path that it follows in operation.